Method of processing mushrooms using starch, gum, protein and water

ABSTRACT

A salt-free treatment liquid for processing mushrooms comprising waxy rice starch, xanthan gum, pure egg white protein and water. After impregnation of the mushrooms, the mushrooms are blanched in water having a temperature of approximately 90° C. to 100° C. In the blancher the treatment liquid jells within the mushrooms, thereby providing a product which has an improved taste, texture and increased yield.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of U.S. patent application Ser. No.07/326,606, filed Mar. 21, 1989, entitled METHOD OF PROCESSING MUSHROOMSUSING RICE STARCH, NATURAL GUM, PROTEIN AND WATER.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to processing mushrooms in general and inparticular to a novel salt-free treatment liquid for impregnatingmushrooms comprising a mixture of starch, gum, protein and water.

2. Description of Prior Art

Various methods have been used in the past to prepare mushrooms forcanning. In one such prior known method the mushrooms are washed andpeeled and then blanched in boiling water for a period of six to tenminutes. The blanching inactives the mushroom enzymes, coagulates themushroom protein and expels the air therefrom due to shrinkage.

Disadvantages of this method are that the volume of the mushrooms isreduced, soluble aromas are reduced, mushroom albumin is reduced and themushrooms undergo a significant weight loss. In addition, it has beenfound that there is a tendency for the mushrooms to turn grayish-brownduring sterilization and blacken when they are exposed to air after thecan in which they are stored is opened.

To reduce the above-described loss of weight, color, taste and textureof the mushrooms, various vacuum processes were developed in which themushrooms are impregnated with treatment liquid comprising water and/ora variety of ingredients.

In one such prior known vacuum process the mushrooms are subjected to avacuum and impregnated with a treatment liquid comprising a mixture ofwater or mushroom juice obtained from boiling mushrooms in water and acolloidal substance selected from the group consisting of egg white,casein, milk albumin (lactalbumin) and carrageenan.

In the prior known vacuum process described above, which is disclosed inU.S. Pat. No. 4,328,251, issued to Blanchaud et al, the colloidalsubstance in the treatment liquid, e.g. egg white, comprised between 10%to 25% by weight relative to the weight of the treatment liquid. Themushroom juice and/or water and the colloidal substance in the treatmentliquid are thoroughly homogenized through slow agitation or byultrasonics. After the mushrooms are placed in a vertical or inclinedvacuum chamber, the chamber is evacuated to a pressure on the order of50 to 60 mm Hg for a relatively long period of time on the order of 6 to10 minutes to remove air and other gases present in the interstices ofthe mushrooms. At the end of the vacuum treatment, the treatment liquidis drawn into the vacuum chamber by the vacuum in the chamber to coverthe mushrooms with the treatment liquid. After releasing the vacuum, themushrooms are permitted to remain in the treatment liquid for a periodof 5 to 10 minutes. Following the impregnation, the mushrooms areremoved from the vacuum chamber, thoroughly washed in running water andblanched in boiling water for 6 to 10 minutes to coagulate the colloidalsubstance impregnated in the mushrooms.

In two earlier patents disclosing substantially the same vacuum process,U.S. Pat. No. 4,218,484 and U.S. Pat. No. 4,143,167, issued to thepatentees of U.S. Pat. No. 4,328,251, the patentees also teach that thevacuum treatment period should be of a relatively long period of time onthe order of 1 to 10 minutes, 2 minutes being usually sufficient, andthat greater vacuums and longer vacuum treatment periods result inlittle, if any, improvement in the mushrooms. The patentees also teachthat the optimum treatment liquid is characterized by a mixture ofapproximately equal parts of water and mushroom juice and a colloidalsubstance comprising 60 grams/liter of finely divided egg white or 280to 420 grams/liter of liquid egg white. In an example of the results ofusing the process disclosed in the earlier patents, the patenteesdisclose that upon completion of the process, the weight of 1000 gramsof mushrooms impregnated with the liquid treatment was reduced to 687grams after the blanching treatment, i.e. a yield of about 69%.

In U.S. Pat. No. 4,735,813, issued to Spinoglio, there are disclosedother vacuum processes using treatment liquids for processing a varietyof vegetables comprising mixtures of proteins and starches, such as ricestarch, dispersed in 2% salt water. In this process, after a briefthermal treatment, the mushrooms are rapidly cooled to gel the starchesin a superficial part of the mushroom so as to form a seal. In stillanother vacuum process, in which actually appears to be a modificationof the foregoing process, there is disclosed the use of ingredients forseasoning and/or enriching in nutritional elements, which may alsoinclude thickening agents such as starches and gums. This process,however, also appears to require the formation of a gel in thesuperficial part by rapid cooling so as to seal the mushroom or othervegetable being processed.

While providing an improvement over the prior known simple blanchingprocess, the treatment liquids used in the above-described vacuumprocesses are found to have a number of disadvantages. For example, theuse of egg white as a colloidal substance in the amounts indicated isvery costly. The use of mushroom juice in the treatment liquid requiresthe additional step of boiling mushrooms to obtain the stock necessaryto prepare the treatment liquid. The need for rapidly cooling themushrooms to form a gel in a superficial part thereof is considered tobe time consuming, costly and not particularly effective for maintaininga high yield. Furthermore, the use of salt in a treatment liquidsignificantly impairs impregnation and adversely affects yields.

The treatment of mushrooms with egg white in the amounts and in themanner disclosed produces a finished, canned product with a packingbrine which contains visible amounts of feathery, coagulated albumin,similar in appearance to egg-drop soup. This feathery brine is perceivedas undesirable by users of the canned product. The use of egg whitealone, in addition to the high cost involved, produces mushrooms havinga bland taste. The use of casein derived from dairy products orlactalbumin alone produces bad flavors. The use of water alone or starchand carrageenan (gum) alone produces a poor yield.

SUMMARY OF THE INVENTION

In view of the foregoing, a principal object of the present invention isa novel salt-free treatment liquid for use in high vacuum processing ofmushrooms which, in comparison with prior known treatment liquids,provides a yield as good as that which can be achieved using 10% pureegg white protein but at far less cost, i.e. less than one third thecost at current prices, while providing a mushroom having an excellentcolor, taste and texture.

In accordance with the above object there is provided a salt-freetreatment liquid comprising by weight 3% to 7% waxy rice starch, 2% to5% pure egg white protein, 0.03% to 0.10% xanthan gum and water.Preferably, the amount of starch, egg white, and gum used is 5%, 2.5%and 0.05%, respectively.

The above-indicated preferred formulation of 5% starch, 2.5% egg whiteand 0.05% gum for the treatment liquid of the present invention producesa yield of around 91%, about the same as produced with 10% egg white,which is much larger than the yield which can be obtained using wateralone, starch alone or starch and gum alone.

The following table shows that a simple blanching process for 100 poundsof mushrooms provides a yield of about 60% as follows:

    ______________________________________                                        Washing           +10% =   110 lbs.                                           Blanching         -35% =   71.5 lbs.                                          Slicing           -6% =    67.21 lbs.                                         Sterilizing       -10% =   60.48 lbs.                                         ______________________________________                                    

The above table provides that for each 100 lbs of mushrooms, washingthem increases their weight by 10%, i.e. from 100 lbs to 110 lbs.Thereafter, blanching the mushrooms causes them to lose 35% of theirweight, reducing their weight from 110 lbs. to 71.5 lbs. Slicing causesan additional 6% loss in weight, i.e. from 71.5 lbs. to 67.21 lbs., andsterilizing then produces still another loss in weight of 10%, from67.21 lbs. to 60.48 lbs.

Tests show that higher yields can be obtained if the mushrooms areimpregnated with a treatment liquid by means of a vacuum. The treatmentliquid may comprise, for example, water alone, gum alone, starch and gumand dry egg white alone. The following tables show the yields obtainedusing such treatment liquids:

    ______________________________________                                        1.   Water alone:                                                                  Washing               +10% =   110 lbs.                                       Impregnation          +50% =   165 lbs.                                       Blanching             -55% =   74 lbs.                                        Slicing               -6% =    69 lbs.                                        Sterilizing           -10% =   62 lbs.                                   2.   With gum:                                                                     Washing               +10% =   110 lbs.                                       Impregnation          +35% =   148 lbs.                                       Blanching             -48% =   77 lbs.                                        Slicing               -6% =    72 lbs.                                        Sterilizing           -10% =   65 lbs.                                   3.   With starch and 0.05% xantham gum:                                            Washing               +10% =   110 lbs.                                       Impregnation          +50% =   168 lbs.                                       Blanching             -50% =   82 lbs.                                        Slicing               -6% =    77 lbs.                                        Sterilizing           -10% =   69 lbs.                                   4.   10% dry egg-white alone:                                                      Washing               +10% =   110 lbs.                                       Impregnation          +40% =   154 lbs.                                       Blanching             -30% =   107 lbs.                                       Slicing               -6% =    101 lbs.                                       Sterilizing           -10% =   91 lbs.                                   ______________________________________                                    

A test was also made to determine the yields obtained using 5% waxy ricestarch alone and 2.5% egg white alone. The yields obtained were 69.7%and 75%, respectively.

As discussed above, a principal advantage of the present invention isthat a significant increase in yield can be obtained using apredetermined amount of egg white and starch in combination atsignificantly less cost than using egg white alone.

As seen in the following table, a treatment liquid comprising 5% starch,2.5% dry egg white and 0.05% xantham gum produces the following yieldsfor each 100 pounds of mushrooms:

    ______________________________________                                        Washing           +10% =   110 lbs.                                           Impregnation      +40% =   154 lbs.                                           Blanching         -30% =   107.8 lbs.                                         Slicing           -6% =    101.3 lbs.                                         Sterilizing       -10% =   91.19 lbs.                                         ______________________________________                                    

The above figures represent the results obtained under industrialconditions. Laboratory results are generally 15% better, i.e. producingan average yield of about 105 lbs. for every 100 lbs. of mushrooms.

As will be noted from the above table, the impregnation of 100 pounds ofmushrooms after they have been washed further increases their weight by44 lbs., i.e. from 110 lbs. to 154 lbs. Using the above increase inweight and the percent of total weight used for each ingredient, thecost of the treatment liquid per 100 lbs. of mushrooms is calculated asfollows:

    ______________________________________                                        Starch  5% × 44 lbs. =                                                                        2.2 lbs. × 0.65 =                                                                     $1.43                                     Egg white                                                                             2.5% × 44 lbs. =                                                                      1.1 lbs. × 5.75 =                                                                     $6.32                                     Xantham 0.05% × 44 lbs. =                                                                     0.022 lb. × 7.00 =                                                                    $0.15                                                                         $7.90                                     ______________________________________                                    

In contrast, the cost of the egg white required to produce the sameyield, i.e. 91%, for each 100 lbs. of mushrooms is calculated asfollows:

    Eggwhite10%×44 lbs.=4.4lbs×5.75=$25.00

One of the principal reasons discovered for the low yields obtained withprior known treatment liquids has to do with the fact that duringblanching the mushroom protein coagulates, causing the mushroom toshrink at a temperature which is generally 6-8° C. lower than thetemperature of coagulation of gelling of typically used impregnatingsubstances. For example, the start of the coagulation of mushroomprotein generally occurs at a temperature of about 60° C., whereas thetemperature of gelling of starch begins around 68° C. Because of thedelayed gelling of the starch, there is a tendency for the mushroomshrinkage to expel much of the starch impregnating liquid before thestarch gels.

In investigating the superior results obtained using the treatmentliquid of the present invention, it was found that the temperature ofcoagulation of the pure egg white therein was approximately the same asthe temperature of coagulation of the mushroom protein. Thus, it wasfound that the coagulation of the egg white, even in the relativelysmall amount used, produces a coagulum early in the blanching processwhich has the beneficial effect of preventing the expulsion of thestarch from the mushroom before it gels.

A further benefit of the relatively small amount of egg white which isused in the treatment liquid of the present invention is that no residuethereof appears in the brine of the mushrooms canned therewith.

Following the preparation of the treatment liquid using chilled water,the mushrooms are placed in a vacuum chamber and subjected to a highvacuum on the order of less than 10 mm Hg for a period of time, e.g.30-60 seconds, sufficient to remove from 98% to 99% of the air and gasesfrom the interstices in the mushrooms. At the end of the vacuumtreatment and while maintaining the pressure within the vacuum chamberat a pressure of less than 10 mm Hg, the treatment liquid is introducedinto the chamber in an amount sufficient to submerge the mushrooms. Oncethe mushrooms are fully submerged in the treatment liquid, the pressurein the vacuum chamber is raised to a higher pressure, e.g. atmosphericpressure or greater. Thereafter, the mushrooms are allowed to remain inthe treatment liquid for a period of time, approximately 10-60 seconds,until they are fully saturated with the treatment liquid. Followingimpregnation, the treatment liquid is drained from the chamber, themushrooms are removed from the chamber and blanched.

In blanching the mushrooms, the mushrooms are submerged in and gentlymoved through a trough of boiling water for a period of time, e.g. 6 to15 minutes, sufficient to create a gel of the treatment liquid containedwithin the mushrooms.

After blanching, if the cooked mushrooms are to be sliced or diced, theyare cooled via water sprays and/or immersion to approximately 30° C. to40° C. and then mechanically sliced or diced. For whole mushroom packs,the cool-down steps and slicing and dicing steps are eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof the accompanying drawings in which:

FIG. 1 is a general schematic of major line components for processingand canning mushrooms using a treatment liquid according to the presentinvention;

FIG. 2 is a top plan view of conventional vacuum impregnation andtreatment liquid holding apparatus for impregnating mushrooms with atreatment liquid according to the present invention;

FIG. 3 is an end view of the vacuum impregnation apparatus of FIG. 2;

FIG. 4 is a side view of the vacuum impregnation apparatus of FIG. 3;

FIG. 5 is a side view of a blancher according to the present invention;and

FIG. 6 is a top plan view of the blancher of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown a continuous vacuum mushroomprocessing line comprising in sequence a washing and sorting apparatus 1for washing and sorting the mushrooms, a vacuum impregnation apparatus 2for impregnating the mushrooms with a treatment liquid in accordancewith the present invention as will be described in more detail below, ablanching apparatus 3 for creating a gel of the treatment liquid in themushrooms after impregnation, a cooling and slicing apparatus 4 forcooling and slicing the mushrooms after blanching, a filling, briningand check weighing apparatus 5 for packing the mushrooms in cans, anexhausting (preheating) apparatus 6 for expelling air from the cans, acan closing machine 7 and a retort apparatus 8 for sterilizing thefinished product.

Referring to FIGS. 2-4, in which the same numeral will be used fordesignating the same feature, there is provided in the vacuumimpregnation apparatus 2 a plurality of refrigerated holding tanks 10for holding a treatment liquid to be described below, an insulated surgetank 11 for holding the treatment liquid, a pipe 17 for transporting thetreatment liquid from the holding tanks 10 to the surge tank 11, aplurality of horizontal cylindrical vacuum chambers 12 and 13, basketconveyors designated generally as 14 for conveying baskets of washedmushrooms as well as empty baskets, a vacuum pump and venturi boosterapparatus 15, and a vacuum pump drive motor 16.

Referring to FIG. 3, there is further provided in the insulated surgetank 11 an inlet 20 coupled to the pipe 17 for receiving therefrigerated treatment liquid from the refrigerated holding tanks 10. Inthe basket conveyor 14 there is provided a lower roller conveyor 21 forconveying full baskets 18 of washed mushrooms and an upper rollerconveyor 22 for conveying empty baskets 19. Attached to each of thehorizontal vacuum chambers 12 and 13 there is provided a liquid leveland vacuum surge tank 23 and 24, respectively. Interconnecting the surgetanks 23 and 24 to the vacuum pump drive motor 16 there is provided avacuum supply line 25. Extending from the surge tanks 23 and 24 there isprovided a vacuum release vent valve 26 and 27, respectively, and avacuum gauge 28 and 29, respectively. The horizontal vacuum cylinders 12and 13, roller conveyors 21 and 22 and surge tanks 23 and 24 aresupported over the surge tank 11 by means of a frame designatedgenerally as 30.

Referring to FIG. 4, there is further provided for interconnecting thevacuum chambers 12 and 13 and the surge tank 11 a plurality of fillingvalves 35 (only one of which is shown) for transporting the treatmentliquid from the surge tank 11 into the vacuum chambers 12 and 13 and aplurality of drain valves 36 (only one of which is shown) for drainingtreatment liquid from the vacuum chambers 12 and 13 into the surge tank11. At the front end of each of the vacuum chambers 12 and 13 there isprovided a vacuum chamber door 37 and 38, respectively. Located in thevacuum supply line 25 there is provided a plurality of vacuum valves 39(only one of which is shown) for coupling and decoupling the vacuumchambers 12 and 13 and liquid and vacuum surge tanks 23 and 24 to andfrom the vacuum pump 15. A plurality of valves is used so that eachchamber can be used separately.

Referring to FIGS. 5 and 6, there is provided in the blanching apparatus3, a water-filled feed tank 45, a metering feed elevator 46 and hotwater deluge pans 47. The pans 47 are connected to a source of hot waterby means of a hot water recirculation pipeline 48. Included in thepipeline 48 there is provided a hot water recirculation system steaminjection chamber 49 for injecting steam into the hot waterrecirculation system. For heating the blancher water along the length ofthe blancher there is provided a steam injection manifold 50 forinjecting steam into the blancher water at various points along thebottom of the blancher. In the interior of the blancher there isprovided a plurality of divider baffles 55 which are coupled to carrierchains (not shown) for moving mushrooms through the blancher. A drivesystem 56 is provided at one end of the blancher for driving the dividerbaffles and carrier chain assembly 55. Located adjacent to the drivesystem 56 there is provided a hot water discharge and surge tank 57. Arecirculation pump 58 is coupled to the tank 57 and the hot waterrecirculation system pipeline 48 for transferring hot water to thedeluge pans 47. Located above the discharge and surge tank 57 there isprovided a discharge elevator 60.

As will be further described below, in normal operation the blancherwater level is sufficient to cover the mushrooms moved therethrough, asshown by the arrow 61 in FIG. 5.

As indicated above, the processing of mushrooms according to the presentinvention using the apparatus shown in FIGS. 1-6 involves thepreparation of a treatment liquid. The treatment liquid is preparedusing mixing equipment to blend in a blending tank waxy rice starchhaving a particle size of from 2 to 8 microns, pure protein, such as eggwhite, natural gum, preferably xanthan, and water chilled to atemperature of less than 6° C. Pure protein means isolates which containa minimum of 85% protein. The mixing equipment and blend tank (notshown) are of a design which imparts high shear and turbulence to theliquid mixture while minimizing air entrainment, such as "Lightnin"mixers with high shear impellers.

The percentage weights of the above-listed ingredients to the totalbatch weight of the treatment liquid are as follows:

    ______________________________________                                        (a) waxy rice starch                                                                          3% to 7%                                                      (b) pure protein                                                                              2% to 5%                                                      (c) natural gum 0.03% to 0.10%                                                (d) chilled water                                                                             88% to 95%                                                    ______________________________________                                    

The timing and order of addition of the above-listed ingredients isimportant to the functional properties of the treatment liquid. Afteradding a measured amount of chilled water to the blending tank, the waxyrice starch is added and mixed for about 10 minutes to avoid clusteringof the starch. The gum, which is pre-blended with 2 times its weight ofrice starch to aid dispersion, is then added slowly to the mixture ofthe rice starch and water. The pure protein is then added and the mixingis continued for about another 5 to 10 minutes until the treatmentliquid is smooth.

After the treatment liquid is formulated as described above, the liquidis transferred to refrigerated holding tanks 10 and held at 2° C. to 6°C.

Referring again to FIG. 1, in practicing the process of the presentinvention, fresh refrigerated mushrooms are washed, inspected and sortedto remove defects, foreign material and off-sized units in the washerand sorting apparatus 1. Preferably, the mushrooms are refrigerated to atemperature of from 2° C. to 6° C. The washed and sorted mushrooms arethen transferred into the baskets 18 and transported to the horizontalcylindrical vacuum chambers 12 and 13 for vacuum impregnation by thetreatment liquid prepared as described above.

In the impregnation cycle, the vacuum chambers 12 and 13 are loaded withthe washed mushrooms, sealed and evacuated by means of the vacuum pump15 via the surge tanks 23 and 24 to a pressure of less than 10 mm Hg fora period of time, approximately 30 to 60 seconds, sufficient to remove98-99% of the entrained air and gases in the mushrooms. After theevacuation cycle, and while maintaining the pressure in the vacuumchamber at less than 10 mm Hg by leaving the vacuum valve open to theappropriate surge tank 23 or 24, respectively, the valve 35 is openedwhich allows the introduction of the chilled treatment liquid into thevacuum chambers in an amount sufficient to fully flood the horizontalchambers and a portion of the surge tanks 23 and 24. The liquid isrestricted to the lower portion of the surge tanks 23 and 24 so as notto be drawn into the vacuum piping and pump 15. The amount of time forthe introduction of the treatment liquid into the vacuum chamber isapproximately 25-30 seconds, depending on the size of the fill pipe andinterior volume of the horizontal chambers. Once the mushrooms are fullysubmerged in the treatment liquid, the pressure in the vacuum chamber israised to a higher pressure, typically atmospheric pressure or greater.The mushrooms are then allowed to remain in the treatment liquid forapproximately 10 to 60 seconds to enable complete saturation of themushrooms at the higher pressure. The treatment liquid is then drainedfrom the vacuum chamber by means of the valve 36. This takesapproximately 30 seconds. The vacuum chamber is then opened and theimpregnated mushrooms are removed. It should be noted that in order tokeep the treatment liquid from boiling in the vacuum chamber, thetemperature of the treatment liquid being introduced into the vacuumchamber should be kept below 6° C.

After the mushrooms are removed from the vacuum chambers 12 and 13, theyare transferred into the blancher 3 by way of the water-filled feed tank45. In the blancher 3, the saturated mushrooms are gently submerged inboiling water by means of the elevator 46. The deluge pans 47 areprovided to deluge the mushrooms with boiling water to very quickly heatthe chilled mushrooms in order to prevent loss of the treatment liquidby creating a gel of the treatment liquid contained within themushrooms. The blancher 3 is able to heat the mushrooms very quicklywhile the divider baffles 55 move them gently and with positive flowcontrol through the blancher. The temperature of the blancher water ispreferably 90° C. to 100° C. The mushrooms remain in the blancher 3 forapproximately 6-15 minutes depending on their size. Thereafter, themushrooms are gently discharged from the blancher 3 by means of theelevator 60.

Following blanching, the mushrooms are further processed depending uponwhether they are going to be used in a sliced pack, used in a wholemushroom pack, canned or frozen. For the sliced pack, the cooledmushrooms are cooled via water sprays and/or immersion in the coolingapparatus 4 to approximately 30° C. to 40° C. and then mechanicallysliced. For whole mushroom packs, the cool-down and slicing steps areeliminated. For the canning process, the mushrooms are deposited intocans, check-weighed and topped with a suitable salted and acidifiedbrine in the filling, brining and check weighing apparatus 5. By analternative method, dry salt and acidulant are first added to the emptycans, followed by the mushrooms and hot water topping of the cans. Fromthe apparatus 5 the canned mushrooms are transported through theexhausting apparatus 6 for preheating, and double-seam sealed in theclosing machine 7. The sealed cans are then sterilized in conventionalsteam retorts 8 and cooled. For freezing, the cooked mushrooms arecooled, sliced or diced and then frozen in conventional individuallyquick-frozen apparatus and packaged.

While a preferred embodiment of the present invention is disclosedherein, it is contemplated that various modifications may be made in thesteps of the process and the apparatus used without departing from thespirit and scope of the present invention. For example, while 5% byweight of waxy rice starch having a particle size of from 2 to 8 micronsis known to be suitable, it is possible that other starches having anequivalent range of particle sizes may also be effective. Similarly,while 2.5% by weight of egg white is known to be suitable for use withthe starch, it is possible that other proteins may also be suitable solong as they have a coagulation temperature substantially equal to orlower than the coagulation temperature of the mushroom protein.Accordingly, the scope of the present invention should not be strictlylimited to the steps and apparatus disclosed but be determined byreference to the claims hereinafter provided.

What is claimed is:
 1. A salt-free treatment liquid for impregnatingmushrooms comprising:a predetermined amount which falls between 3% and7% by weight of the treatment liquid of waxy rice starch having aparticle size of from 2 to 8 microns; and a predetermined amount whichdoes not exceed about 5% by weight of the treatment liquid of proteinhaving a temperature of coagulation which is substantially equal to orlower than the temperature of coagulation of the natural mushroomprotein in said mushrooms, the amount of protein being sufficient sothat on the mushroom being heated to the temperature of coagulation ofthe natural mushroom protein in the mushrooms the protein coagulatesthereby preventing expulsion of the starch from the mushrooms for a timesufficient for the starch to gel within the mushrooms.
 2. A salt-freetreatment liquid for impregnating mushrooms according to claim 1 whereinsaid protein comprises egg white.
 3. A salt-free treatment liquid forimpregnating mushrooms according to claim 2 wherein said predeterminedamount of said waxy rice starch comprises from 3% to 7% by weight ofsaid treatment liquid, said predetermined amount of said egg whitecomprises 2% to 5% by weight of said treatment liquid.
 4. A salt-freetreatment liquid for impregnating mushrooms according to claim 2 whereinsaid predetermined amount of said waxy rice starch comprises 5% byweight of said treatment liquid and said predetermined amount of saidegg white comprises 2.5% by weight of said treatment liquid.
 5. Asalt-free treatment liquid for impregnating mushrooms according to claim1 further comprising a predetermined amount of gum for holding said waxyrice starch in suspension in said treatment liquid.
 6. A salt-freetreatment liquid for impregnating mushrooms according to claim 5 whereinsaid gum comprises xanthan gum and said predetermined amount of xanthangum comprises from 0.03% to 0.10% by weight of the treatment liquid. 7.A method of processing mushrooms comprising the steps of:preparing amixture of natural gum, waxy rice starch and chilled water by mixing aselected amount of natural gum and a selected amount of waxy rice starchin a measured amount of chilled water for approximately 10 minutes, saidchilled water having been chilled to a temperature of from 1° C. to 5°C.; preparing a salt-free treatment liquid comprising a mixture ofnatural gum, waxy rice starch, chilled water and pure egg white proteinby mixing in equipment which imparts high shear and turbulence to thetreatment liquid a selected amount of pure egg white protein in saidmixture of natural gum, waxy rice starch and chilled water forapproximately 10 minutes until said treatment liquid is smooth, thepercentage weight of the ingredients of said treatment liquid to thetotal batch weight being as follows:

    ______________________________________                                        (a) waxy rice starch                                                                            3% to 7%                                                    (b) pure egg white protein                                                                      2% to 5%                                                    (c) natural gum   0.03% to 0.10%                                              (d) chilled water  88% to 95%;                                                ______________________________________                                    

maintaining the temperature of the treatment liquid within a range fromabout 2° C. to about 6° C.; cooling a batch of mushrooms to atemperature which falls in a range from about 2° C. to about 6° C.;subjecting the mushrooms to a vacuum at a pressure of less than about 10mm Hg for a period of time sufficient to remove about 98% or more of theentrained air and gases from the mushrooms; contacting the treatmentliquid with the mushrooms in an amount sufficient to fully cover themushrooms while maintaining the pressure at less than about 10 mm Hg;raising the pressure to or above atmospheric pressure; allowing themushrooms to remain in the treatment liquid for a time sufficient toenable complete saturation of the mushrooms at the higher pressure;separating the treatment liquid from the mushrooms; and blanching themushrooms with blancher water at a temperature of between about 90° C.and 100° C.
 8. A method as set forth in claim 7, furtherincluding:sterilizing the blanched mushrooms.